Numerous progressive lenses are known in the prior art. Progressive lenses have heretofore been designed on the basis that they have distance, near and intermediate viewing zones. The intermediate zone joins the near and distance zones in a cosmetically acceptable way, in the sense that no discontinuities in the lens should be visible to people observing the lens of the wearer. The design of the intermediate zone is based on a line called the "eye path" along which the optical power of the lens increases more or less uniformly. It is normal to select an eye path to accommodate an assumed convergence of the eyes along the path beginning at a fitting cross in the distance zone and slanting nasally to the near zone.
Applicants have noted that most known progressive lenses are designed based on
1) eyepaths which are optimised in the near viewing region for a refraction distance of 30 cm or closer, a distance at one extreme of the normal range, and PA1 2) eyepaths based on conventional assumptions concerning accommodation converging movement, which do not account for use of the wearer's accommodative reserve, and that PA1 3) the overall design of conventional progressive lenses do not achieve the same balance of useful optical fields of vision for different categories of patients, e.g. myopes, emmetropes and hyperopes. PA1 a) designing a series of progressive lens blanks in which two or more of the lenses have substantially the same addition power and a shared performance characteristic(s) but differ in base curve in order to provide for the differing distance prescriptions of differing categories of patient, including myopes and emmetropes; PA1 b) obtaining a prescription for the patient including a required distance prescription and cylinder correction; PA1 c) selecting a progressive lens blank from the designed series on the basis of distance prescription and cylinder correction thereby obtaining the shared performance characteristic regardless of the category of patient; and PA1 d) finishing the back surface of the lens blank to obtain the prescribed distance prescription and cylinder correction. PA1 a) providing a mathematical or numerical representation of a progressive lens surface having a distance viewing zone, a near viewing zone and an eye path corridor wherein the eye path corridor is centered on a line of approximately zero surface astigmatism and has a progressively varying refractive power. PA1 b) rotating and horizontally off-setting the representation of the lens surface below the distance viewing zone in a nasal direction to account for accommodative reserve and the variation of inset caused by the progressive power increase in the eye path corridor; PA1 c) rotating the representation of the lens surface below the eye path corridor in a temporal direction; PA1 d) modifying the representation of the lens surface on the basis of the location of horizontal mid-points between nasal and temporal isoastigmatism curves of a selected dioptric value; and PA1 e) forming a lens surface corresponding to the modified representation of the lens surface.
Accordingly, it would be a significant advance in the art if the progressive lens could more closely relate to the requirements of the individual wearer. It would be a further significant advance if the optimisation of the near viewing region could be altered to a more representative near refraction distance. It would be yet a further advance in the art if a series of progressive lens elements provided the same balance of useful optical fields for different categories of patients.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties and deficiencies related to the prior art. These and other objects and features of the present invention will be clear from the following disclosure.